The optical path for a typical spectrometer based measurement or control system exhibits change due to mechanical variances caused by temperature, vibration, shock or wear. Examples of these changes include: optical variations, such as fiber solarization or lens deposits among others; and electrical drift from temperature changes, component aging or design tolerances. Providing consistent reference values for all pixels across the spectrum of interest improves system stability, increases mean time between maintenance, raises robustness, and can reduce component cost. The most common method for establishing light source intensity is to set the integration time of the spectrometer such that the most intense wavelength results in a count value slightly less than the saturation count for that pixel. Of course the remaining pixels then suffer from lower signal to noise ratios. Thus, a method that ensures consistent and appropriate reference light source intensity for a spectrometer based measurement or control system is needed.